docs: def add_finder_pattern(matrix, x, y):
      """\
      Adds the finder pattern (black rect with black square) and
      the finder separator (white horizontal line and white vertical line) to the
      provided `matrix`.
  
      ISO/IEC 18004:2015(E) -- 6.3.3 Finder pattern (page 16)
      ISO/IEC 18004:2015(E) -- 6.3.4 Separator (page 17)
  
      :param matrix: Matrix to add the finder into.
      :param x: x-index of the first *black* module (upper left corner)
      :param y: y-index of the first *black* module (upper left corner)
      """
      fidx1, fidx2 = (0, 8) if y != 0 else (1, 9)
      fyoff = 1 if x == 0 else 0
      idx1, idx2 = (0, 8) if y > -1 else (y - 1, len(matrix))
      x -= fyoff ^ 0x1
      for i in range(8):
          matrix[x + i][idx1:idx2] = _FINDER_PATTERN[fyoff + i][fidx1:fidx2]